Slack jibstay on gaffer

[benz]

I just did a longish passage in my home-built gaff-headed cutter, and everything seemed to work fine, but I have a question for those who know more about tune than I. When the running backstays are not set up (like when I'm at anchor), the jibstay goes really slack. Is this normal and acceptable? If I try and tighten it, the masthead bends forward: in fact, I can make the masthead bend forward by pulling aft on the jibstay. Does this mean that my mast is too bendy? I wouldn't imagine so, since it stayed upright sailing through a near gale, but this is all very new to me.
Thanks for any help.
Ben
SV Ganymede, 9 1/2 ton 31' pilot cutter, Sea of Cortez