Bug while importing in shoot in LR 3.3 Should I discard & reimport?

Question

I just imported a 125 pics shot
1/ copy from CF to a disk folder
2/ import into LR Move,Rename,apply metadatada & develop preset (all included in one of my user import presets)
However pics 13 to 24 appeared all grayed-out in Library module, both in Grid and Loupe view.
When I moved to Develop module AND PASSED OVER EACH OF THESE PICS, they suddenly appeared Ok and are staying as such even when I revert to Library module.
What happened?
Should I consider these pics as ok or would it be better to delete them and start again (or maybe to reimport the whole shoot?)

Answer 1

So the first time you imported the images, a few had gray-with-three-dots instead of the normal thumbnail image even after half-an-hour?  Did you have to switch to Develop before the thumbnails showed up, or did you have to restart LR to have them show up?  It almost sounds like something was wrong with the preview/thumbnail computation or retrieval process and some got missed, but changing something with the images cause them to be recomputed and seem ok.  Is anything still wrong with those images or their previews/thumbnails as far as you can tell, after exiting and restarting LR? 
Either something was a little weird with your computer processes during your import and it causes something to stop some previews from getting rendered or at least not displayed, but won't likely happen very often, or something has caused a little corruption to occur in your catalog or your previews database, and thumbnails getting missed will probably continue to happen as time goes on, or there is a bug with LR or other system drivers that prevent some thumbnails from being display properly and it could keep happening but is not a concern for your photos, themselves, or there is something wrong with your images that will cause those particular ones to always have issues, but others may or may not.
If you have time to experiment, then you might be able to determine which of the above is more likely the case through a process of elimination where the idea is to make a series of small changes to the LR environment in a particular order, to see which ones show the problem and which ones seem to fix it, and by whatever step fixes the problem you'd know where the problem was.
The first thing to do is to create a new catalog and import the 125 photos into it.  This would rule out something being wrong with the photos, themselves, and if you have thumbnail rendering issues with these few photos in a completely empty catalog, then the photos or their location on the hard-disk likely has issues and there's no need to do the other steps.
Assuming the photos aren't at fault, start the experiments by first making a backup of your catalog w/o optimizing or testing for integrity, so you have a backup the way it is, then remove and reimport the entire 125 photos.  If nothing happens wrong with any of the photos, then it's likely just a fluke that something was transiently weird with your system, and it may not happen, again.
If something is wrong after reimporting, then make another backup of your catalog, this time optimizing and testing the integrity, and do the remove/reimport again.  If nothing is wrong this time but was last time, then your catalog may have been slightly corrupted or not being optimized was slowing it down to the point of seeing an effect on preview processing, and who knows what if any settings or adjustments have disappeared for old photos if records had to be deleted to fix the catalog, but it is back to being ok, now.  I have never had anything go wrong with a catalog so don't know if LR tells you if it finds and fixes something or if it just silently fixes it.
If something is still wrong with the photo import after importing into an optimized catalog, then exit out of LR and make a copy of the catalog file with file-system operations without copying the previews (which would take a very long time, unless this is a tiny catalog), and try removing and reimporting into that copy of the catalog.  If things work ok, this time, but didn't the last two times, then something may have been wrong with the previews database.  If you want you could just keep using this new catalog copy, but you could also just go and delete all the previews data from the original catalog location (via file operations outside of LR that don't touch the catalog file, itself) and then open and keep using the original catalog w/o having any issues.
If you continue to have issues with some photos not showing thumbnails, then the problem likely lies with the LR program or somewhere else in your system unrelated to the LR database or previews and this could be harder to troubleshoot.