It’s not normal, but it does depend to a certain degree how far you are bending the string.
But it is not normal for a guitar to lose pitch are a few simple bends.
Things to check for:
Are you winding on the strings correctly? don’t wind the strings around the tuning posts 20 times, this will cause the string to slip under tension.
If you know how to correctly re-string a guitar then try these other tips:
When you change strings use some ‘Nut Sauce’ (a product available to help the string from catching on the nut and saddle ) or you could try Graphite from a pencil and ordinary ‘B’ or ‘4B’ type, just scratch the pencil over the nut a few times til you see the graphite dust laying in the slot and on the saddles.
Is it all strings losing pitch after bends?
Another thing to try try is putting a capo nice and tight on the 2nd fret, then try your bends and see if it goes out of tune, if it stays in tune and you have tried the above tips, then it could be a slipping machine head, replacements are available from allparts.com or .co.uk
Does your guitar have a trem system? if so which type?
Well thats some tips to be getting on with,
Let us know how you get on,
Good luck.