Timesheet : charging not possible on project

Good morning,
I have a question about timesheets.
I have a project created with one developer assigned and declared on it.
For the first time this morning he tried to declare his timesheet. Cells were available. He entered a 0.13 value for a meeting with a Ctrl+S just after. 
just after the saving, all cells are now inaccessible. (see screenshot)
We can see that he has assigned work today and yesterday....

I probably did something wrong with the rights (but I don't see).
Why cells are not accessible ?
Any idea?
Many thanks.

Strange behaviour, if in the properties I check the box "cacher les éléments non commencés" then I can fill the time.
If unchecked, no possible action
See screenshot
My version 10.1.4
 

I'm OK with your last message, but I do not understand why (for the same activity) :
- I can enter time when the filter is "on"
- I cannot enter time when the filter is "off"
The activity is in progress...

Hello,
I am sorry but I do not understand your answer. Just to summarize a bit my issue :
- I have a started activity in the workflow
- For the week, I have planified job to enter in the timesheet

It is in read only. If I click on the "hide not started activity", I can enter some time. But here, the filter has not effect because the activity is already started.

I have then a read only without filtering but read/write with a filter wich has nos effect (on hiding things) except allowing RW.

Normally, I should have the possibility to enter time without any filter.....
Really strange.
Many thanks.