my rarity support gems bonus decreased

A level 6 Increased Item Rarity support gem should have 40%, not 50% bonus. It could be higher with quality, but not enough to get to 50%, even with max quality.

If you were looking at the total in the character panel, that will include IIR from gear as well, which might be where the extra 10% came from.

This gems was nerfed in a previous patch (0.9.8). This was described in the patch notes at the time (towards the end of march, before the open weekend). The first time you loaded your character after that patch, the value would have been reduced to the current value - it can't be delayed and happen when you unsocket as you describe, but it's possible you might have remembered the old value and not noticed the change until you unsocketed the gem, if this is the first time you've loaded that character since that patch.

In future, please don't duplicate the report so much. it is not necessary to PM me, and to post this in two different places - the post in the feedback thread for this gem was enough.