As per my info Comodo antivirus does not scan files for malwares while CAV is updating itself if this is true, please make some changes so that antivirus can scan for malwares even when CAV is updating. if my info regarding this is wrong then i appologize:)
AFAIK, this is true for pretty much all AVs, not just Comodo.
The internal databases used for prevention or detection are what is being updated (generally) and these would need to be held in a known state for the update to complete.
One alternative would be to temporarily disable all internet data transfers with the exception of the update site. While this would work, it would be best achieved by an integrated suite like CIS where the AV can internally communicate with the firewall that it is about to attempt an update download and have the firewall component temproarily suspend all addressses other than the one specified by the AV module.
This method would only be achievable by a suite where there are known, trusted internal communication channels between the AV, the AV updater and the firewall.
Similarly, you can’t work on a cars motor without turning it off.
Cheers,
Ewen 
Panic is correct, no other AV will scan while updating. Usually they will update prior (default setting) to any scan. Since the database is in a state of change, it cannot be used to scan at that moment. This is not a flaw in the programming.
Someone previously suggested downloading the file separately, and once it finishes downloading, disable the engine and replace the file (minimizes the downtime/risk). I think that would be the best option
Actually that would be a good idea, if it isn’t already being implemented.
mjj09 Exactly That be best idea to be implemented according to me also