YANBU.
I can see the temptation in waiting until you have been on IS for 6 months before getting a job.
After 6 months, not only do you get a back to work bonus, but you also get 4 weeks of housing benefit and council tax benefit paid too, not to mention the CTC, WTC, CB, and wages too.
Also, the job you are starting, if it is indeed after 6 months on IS, only needs to be expected to last you 5 weeks or more.
If your job unfortunately doesn't work out (for whatever reason, jobcentre don't ask reasons when it comes to IS, and if they do, you have no obligation to give them a reason) before the 5 weeks is up, well you get to keep your nice little back to work bonus, all benefits are resumed, and yr IS will only be reduced by how much WTC you get.
So you could go for a job every 6 months, believing it is going to last at least 5 weeks, and hey presto, a nice little bonus.
After 12 months on benefits, you are right, as well as the 6 monthly bonus, you get a £40 a week bonus, tax free every week for a year, that doesn't affect your HB/CTB/tax credits etc etc.
I have heard that after 18 months on benefit, you are entitled to a 3 monthly bus pass too, which if you find a job just after receiving your bus pass, there is no obligation to return the bus pass, and you can use it to get to your new job for the first 3 months.
Of course, if you are lucky enough to find a job sooner than 6 months, there's no such help for you.
I often wondered if it would be a better idea to offer all of this if you managed to find work in under 6 months, on the basis that you could only claim the help maximum of once or twice a year perhaps?