Has this ever happened to you. You have a heavy racket but when you use a very light racket then transfer back to your heavy racket, your heavy racket seems as light as the racket you last used.

yes, it happened to me

hmmmm...... never happen to me before.
May be just only your mindset.
dunno

Do you mean an actual heavy (ie total mass) racket or heavy-feeling (ie head heavy) racket?

At the end, it's the difference in total mass that causes this phenomenon. If you use a heavy but head-light racket (which normally "feels" light) then switch to a lighter but head-heavier racket (which normally "feels" heavy), the latter will "feel" lighter as your body is still accustomed to the weight of the previous racket.

I actually do this myself... heavy, headlight racket to warm up... then lighter, head-heavier racket for the game... Not generally recommended though as you also have to accommodate the difference in playability of the rackets. If you can adjust fast enough, it can't backfire...

Assuming balance is the same with both rackets and you use a light racket first then heavy racket after... And the heavy racket feels lighter just baffles me...

Nope, i think it is mindset, If i used a heavier racquet n switch to a lighter one or vice-versa, the timing will need to adjust.

It could be that your arm just got warmed up. More blood flow and thus more power. I have experienced something similar with running. When I first start for the like the first couple minutes it's pretty hard to get my legs moving. After warming up, it becomes much easier until I get tired hehe.

Nope, its happened the other way around though...when i use a light racquet, then a heavy one and go back, the light racquet suddenly seems even lighter :D :D

When I hold my 3U MP99, it feels moderately heavy. Then I pick up my AT700, and it feels endloaded (but it's still okay). Then I pick up my MP99 and it's like I'm holding a feather.

off course just the feeling, because my arm already warmed up