More than 1 gear

I seem to be able to select more than 1 gear when at a standstill.
If I fiddle with the gear stick when stopped I find that the gearbox is locked SOLID, unable to move even an inch forwards or backwards.
It feels like it's going into gear normally but it's locked solid.
Some judicious waggling of the gear lever and eventually I can select as normal and it'll be fine for days and 100's of miles.
Been underneath all seems well, in fact all seems new 'cos it is.
Only happens if I waggle the stick when stopped?
I am officially confused.com.

 

Stop waggling, you will go blind!

 

This in Ted?

Didn't you put a refurb'd box in?

 

Yes, it's in Ted and yes it's a rebuilt 6 rib with an extra long 4th.
Runs and drives perfect, never crunches when driving, it only happens if I mess around when not running?

 

I'm no expert when it comes to boxes, but I would refer you back to the builder... As it shouldn't be doing that

 

You don't want to end up like me

 

What has happened to your Bern?

 

Stuck in first - some kind of selector issue.

 

Could be the selector rod is slipping out of the front donut shaped sleave at the front chassis.
Tumnus.

 

*U*